Update runner image to 24.04

[balcsida]

This should also enable running all the tests that were skipped due to the old busybox

[Copilot]

Pull request overview

This pull request updates CI to run on Ubuntu 24.04 and refreshes the tox-pinned lint toolchain, with the intent of unblocking BusyBox-based tests that were previously skipped on older runner environments.

Changes:

• Switch GitHub Actions runners from ubuntu-22.04 to ubuntu-24.04 and stop skipping mic/growpart in the BusyBox minimal-environment test step.
• Update tox-pinned versions of flake8, pylint, and shellcheck-py.
• Minor robustness/cleanup tweaks in scripts (context-manager file handling in write-mime-multipart, f-string formatting in ec2metadata, quoting an echo in a test script).

Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tox.ini	Updates pinned linter/tool versions and flattens file lists used by flake8/pylint/shellcheck.
test/test-growpart	Small shell quoting adjustment for consistent output.
bin/write-mime-multipart	Uses context managers for file IO and refactors output writing into a helper.
bin/ec2metadata	Converts several string interpolations to f-strings (including usage text).
.github/workflows/ci.yaml	Moves CI runner to Ubuntu 24.04 and enables BusyBox tests previously skipped due to BusyBox age.

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[paride]

Reviewed commit-by-commit, LGTM, thanks!